Coordinated hydraulic control apparatus



April 26, 1955 R. E. MICHEL 2,706,386

COORDINATED HYDRAULIC CONTROL APPARATUS Filed June 14, 1950 WO'L (DOLER (fi Q Q 473 \I on. SUPPLY PUMP PuMP WW 0 O O O 55 Yl Q i I23 E A I22 45 O TEMP. SENSITIVE o 2e RESISTOR 32 I I57 I56 LO TEMP. i 4 ssuzcroa 1 1 ELECTRICAL H NETWORK |62 1 1 LC 1 |6l INI-"ENTOR.

l RAYMOND E. MICHEL ATTORNEY United States Patent COORDIYATED HYDRAULIC CONTROL APPARATUS Raymond E. Michel, St. Louis Park, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application June 14, 1950, Serial No. 168,089

.13 Claims. (Cl. 6035.6)

The present invention is concerned with an improved hydraulic control system. More particularly the present invention is concerned with a hydraulic control system wherein there is a continuous circulation of hydraulic fluid through a controlled hydraulic servomotor and also where a pair of hydraulic servomotors are slaved together to prevent their getting out of step.

The present invention is particularly adapted for use in the positioning of the shutters or eyelids used to vary the outlet area of a gas turbine engine. These eyelids are used in pairs and are pivoted at the ends thereof on either side of the end of the gas turbine engine with which they are associated, so that rotational movement thereof will vary the area of the outlet of the engine. As these eyelids are light in weight, are subject to sticking, and can be torsionally twisted, it is necessary that their movements be synchronized. If they should get out of step, the exhaust stream of the engine may be acting away from the central axis of the engine and, if the engine is used in a jet propelled craft, the diverted jet stream may throw the craft off course. The present invention provides a pair of servomotors for positioning a pair of eyelids controlling a gas turbine outlet area with an inter-connecting linkage for synchronizing the opera tion of the motors to keep them in step. As the servomotors are generally mounted adjacent to the tail cone section of the engine, they are subject to severe temperature conditions that, if not cared for, will cause destruction of the hydraulic fluid used in the motors. The present invention provides for continuously circulating the hydraulic fluid through the servomotors and passing the fluid through a cooler to remove the heat therefrom.

It is therefore/an object of the present invention to provide a new and improved hydraulic control system wherein the servomotors are slaved together to maintain their outputs in step.

Another object of the present invention is to provide a hydraulic control system wherein a mechanical linkage is used to maintain a pair of hydraulic servomotors in synchronization.

Still another object of the present invention is to provide a new and improved hydraulic control system wherein hydraulic fluid is continuously circulated through a pair of synchronized hydraulic servomotors.

A further object of the present invention is to provide a hydraulic control motor wherein the hydraulic fluid is fed through the motor continuously and with modulating adjustment provided for all of the fluid flow passages connected to the motor.

A still further object of the present invention is to provide synchronized hydraulic control for the eyelids of an outlet area regulator of a combustion engine.

These and other objects of the present invention will be understood upon a consideration of the following specification and the appended drawing.

Figure 1 shows schematically the overall hydraulic control system of the present invention.

Figure 2 shows a side view of the rear end of a combustion engine.

Referring to Figure 1, there is shown the exhaust end of a combustion engine which has a pair of eyelids 11 and 12, the latter being shown in side view in Figure 2, arranged to vary the outlet area of the engine 10. The positioning of the eyelids 11 and 12 is accomplished by a pair of hydraulic servomotors 14 and 15 acting through suitable interconnecting members 16 and 17. The operation of these servomotors may be initiated ice either by an electrical control motor 18 or by a manually positioned lever 19, both acting through a mechanical linkage arrangement indicated generally by the numeral 20 which operates upon a pair of pilot valves 21 and 22, the latter controlling the pressures of the hydraulic fluid acting on the servomotors 14 and 15.

The hydraulic servomotor 14 comprises a cylinder 25 having a piston 26 arranged therein for axial movement. The piston 26 has a rod 27 which is connected to the driving member 16. The cylinder 25 has a pair of inlet ports 28 and 29 and a pair of outlet ports 30 and 31, and is anchored at 32. The hydraulic servomotor 15 comprises a cylinder which houses a piston 36 which is arranged for axial movement within the cylinder. The piston 36 drives a piston rod 37 that is interconnected to the driving member 17. The cylinder 35 has a pair of inlet ports 38 and 39 and a pair of outlet ports 40 and 41 and is anchored at 42.

The pilot valve 21 comprises a cylindrical member 44 having a plurality of feed lines connected thereto and an inner hollow cylindrical ported member 45. The ported member 45 has a pair of supply inlet ports 46 and 47 and a pair of supply outlet ports 48 and 49. The ported member 45 also has a pair of return inlet ports 50 and 51 and a pair of return outlet ports 52 and 53. A valve spool member 55 is used to modulate the cross sectional area of the ports in ported members 45 and the pressure drops of hydraulic fluid in the valve. The spool member 55 comprises; a valve member 56 arranged to modulatingly control the fluid pressure drop between return inlet port 50 and return outlet port 53; an isolating member 57, a valve member 58 arranged to modulatingly control the fluid pressure drop between the supply inlet port 46 and the supply outlet port 48; a valve member 59 arranged to modulatingly control the fluid pressure drop between the supply inlet port 47 and the supply outlet port 49; an isolating member 60; and a valve member 61 which modulatingly controls the fluid pressure drop between the inlet port 51 and the return outlet port 52. A positioning shaft 62 is arranged to move'the spool 55 axially within the ported member 45. A pair of bleed ports 63 and 64 are arranged on either end of the end modulating members 56 and 61 of the spool 55 to prevent the forming of a fluid pocket which would prevent movement of the spool 55.

The construction of the pilot valve 22 is identical to that of the valve 21. This valve comprises a cylindrical housing with a hollow cylindrical ported member 71 formed therein. This ported member has a pair of supply inlet ports 72 and 73 and a pair of supply outlet ports 74 and 75, as well as a pair of return inlet ports 76 and 77 and a pair of return outlet ports 78 and 79. A spool 80 is arranged for axial movement within the ported member 71 to modulate the pressure drop of the fluid across the several ports. The spool 80 comprises: a valve member 81 which is arranged to modulatingly control the fluid pressure drop between the return inlet port 77 and the return outlet port 79; an isolating member 82; a valve member 83 which modulatingly controls the fluid pressure drop between the supply inlet port '73 and the supply outlet port 74; a valve member 84 which modulatingly controls the fluid pressure drop between the supply port 73 and the supply outlet port 75; an isolating member 85; and a valve member 86 which is arranged to modulatingly control the fluid pressure drop between the inlet port 76 and the return outlet port 78. A pair of passages 87 and 88 are used to bleed the left and right ends of the spool 80 to prevent fluid from blocking the movement of the spool 80. A driving or positioning rod 89 is used to connect the spool 80 to the linkage 20.

The linkage 20 comprises a yoke member which is mounted for longitudinal movement by a pair of hinge members 96 and 97. The yoke member has a forked portion with two projections 98 and 99 acting upon a pair of pivoted link members 100 and 101. The link members 101 and 100 are pivoted on the projections 98 and 99 at 102 and 103 respectively. The left end of the member 100 is arranged to be positioned by a followup link 104 which is pivoted at 105, the link 104 having its left end connected by link 106 to the piston rod 27 and its right end connected by a link 107 to the left end of link 100. Similarly, the right end of link 101 is arranged to be positioned by a followup link 108 which is pivoted at 109, the link 108 having its right end connected by a link 110 to the piston rod 37 and its left end connected by a link 111 to the link 101. A pair of links 112 and 113 interconnect the members 100 and 101 to a pivoted member 114 at pivots 115 and 116, said pivots being positioned on either side of the main pivot 117. The main pivot 117 for the member 114 is positioned on a rod 118 which is arranged for longitudinal movement, the rod being supported by guide members 119 and 120.

The ends of pivoted member 114 are connected by links 121 and 122 and bell cranks 123 and 124 to the adjusting rods 62 and 89 of the pilot valves 21 and 22, respectively.

The positioning of the yoke 95 may be accomplished by a crank arm 130 acting through link 131 to position a member 132, the left end of the member being attached to the yoke 95 at pivot 133 and its right end normally held stationary by a support member 134 which is pivotally attached to member 132 and engages a latch member 135. The latch member 135 is pivoted at 136 and is held in latched position and against a stop 139 by a spring 137. A latch release mechanism or toggle 138, when actuated, will move the latch member 135 to the released position. This release mechanism may be operated by a manual operator 140. The right end of the member 132 may be positioned by the manual lever 19 acting through flexible cable device 141 when the support member 134 is released.

An electrical switch 142 is associated with the latch member 135, said switch having a push rod 143 which will actuate the switch to a closed position upon the rod engaging a projection 144 on the support member 134. This switch serves as an interlock between operating the system with a manual mechanical connection and manual electronic connection.

Oil is supplied to the hydraulic system by a pair of positive constant displacement pumps 150 and 151 which may be driven by any suitable driving means, not shown. These pumps continuously circulate hydraulic fluid from the oil supply reservoir 152 through the hydraulic system and then back through an oil cooler 153.

The control apparatus for the motor 18 may be a temperature control apparatus which comprises a balanceable electrical network 155 having a temperature selecting means or temperature selector 156, a temperature responsive reslstor 157 and a followup potentiometer 158. The output from network 155 is fed into an amplifier 160 the output of which is arranged to drive the reversible motor 18. Bridge, amplifier, and

motor combination may be of the type disclosed in the Albert P. Upton patent, 2,423,534, issued July 8, 1947. The power to the amplifier 168 is fed thereto through suitable power leads 161 and 162 connected to a source of power, not shown, and the lead 162 is arranged to pass through the switch 142 so that whenever the switch is closed, the amplifier 160 will be operative. Should it be desirable to provide a brake for the motor, this may be done as is taught in the Lear et al. Patent 2,267,114, issued December 23, 1941.

In Figure 2, it will be noted that the hydraulic servomotor 14 is mounted adjacent the side of the engine and the output rod 27 is arranged to operate eyelids 11 and 12 through links 16 connected as a toggle arrangement, motor 15, not shown, being arranged on the opposite side of the motor and similarly connected P to the eyelids.

Operation In considering the operation of the present arrangement, it should first be assumed that the apparatus is in a balanced condition as it is shown upon the drawing in Figure 1. if the system is in balanced condition. the spools 55 and 80 and their respective members will be covering the ports on the upstream side of the valve of the ported members 45 and 71 by an equal amount so that the effective cross-sectional areas of the ports will be the same. The ports on the downstream side are normally enlarged so that there will be no effective pressure drops at those points. Under these conditions, the pump 150 will be supplying hydraulic fluid to the scrvQ- motor 15 while the pump 151 will be supplying fluid to the servomotor 14. The fluid flow passages associated with the pump 1511 may be traced from the pump 150 through line 170 to the pilot valve 21 where the line is split into two portions and the fluid flow passes to the supply inlet ports 46 and 47. The fluid flow circuit from the supply inlet port 46 may be traced through the pilot valve assembly, out of supply outlet port 48, line 171, motor inlet port 28, motor outlet port 31, line 172, return inlet port 50, return outlet port 53, line 173, oil cooler 153 and oil supply 152 back to the pump 150. The fluid flow circuit continuing from the supply inlet port 47 may be traced through the pilot valve assembly out the supply outlet port 49, line 174, inlet port 29, outlet port 30, line 175, return inlet port 51, return outlet port 52, line 176, oil cooler 153, and oil supply 152 back to the pump 150.

A similar fluid flow circuit may be traced in the other pilot valve assembly and hydraulic valve servomotor. This fluid flow circuit will originate from the pump 151 and will flow through the line 179 to the pilot valve assembly 22 where the line branches out to the supply inlet ports 73 and 72. The fluid flow circuit may be traced from the supply inlet port 73 through the pilot valve assembly and out the supply outlet port 74, line 180, inlet port 38, outlet port 40, line 181, return inlet port 77, return outlet port 79, line 182, oil cooler 153, and oil supply 152 back to the pump 151. The flow circuit from the supply inlet port 72 may be traced through the valve assembly and out of the supply outlet port 75, line 183, motor inlet port 39, motor outlet port 41, line 184, return inlet port 76, return outlet port 78, oil cooler 153, oil supply 152, back to the pump 151.

As long as the ports of the ported members 45 and 71 have the same cross sectional area the pressure drops occurring in the fluid flow lines will be constant and the system will remain in a balanced position.

Assume now that there has been a temperature decrease within the engine 10 so as to effect a change in temperature of the temperature sensing resistor 157. This drop in temperature will be effective to unbalance the network 155 and cause the amplifier 1641 to drive the motor 18. Inasmuch as a drop in temperature within the engine 10 is conventionally corrected by closing the eyelids on the end of the engine 10, it will be necessary to move the piston rods of the servomotors 14 and 15 in an upward direction, or, referring to Figure 2, moving the piston rods toward the left. This movement of the piston rods will be effected by the motor 18 acting through the crank arm 130, link 131, and pivoted member 132 to move the yoke in a downward direction. When the yoke 95 moves in a downward direction the link member will be pivoted in a clockwise direction about its left end and the link 101 will be pivoted in a counterclockwise direction about its right end so that the interconnecting links 112 and 113 will act upon the pivoted member 114 to move it in a downward direction. As long as the forces acting upon the connecting links 112 and 113 are equal the member 114 will not pivot but will be moved along with the main pivot 117, carried by the rod 118. Movement of this pivoted member 114 in a downward direction will cause the link member 121 to pivot the bell crank 123 in a counterclockwise direction and the link member 122 will cause the bell crank 124 to pivot in a clockwise direction. When the crank 123 moves in a counterclockwise direction, the actuating rod 62 of the spool 55 of pilot valve 21 will be moved toward the right. Similarly, the movement of the bell crank 124 in a clockwise direction will cause the actuating rod 89 of the spool 80 of pilot valve assembly 22 to be moved toward the left.

Movement of the spool 55 to the right will affect a change in the cross-sectional area of the upstream ports of the ported member 45. Thus, the valve member 56 will decrease the cross-sectional area of the return inlet port 50 and the return outlet port 53 While the spool member 58 will increase the cross-sectional area of the supply inlet port 46 and the supply outlet port 48. Similarly, the spool member 59 will decrease the cross-sectional area of the supply inlet port 47 and the supply outlet port 49, and the spool member 61 will increase the cross-sectional area of the return inlet port 51 and the return outlet port 52. This movement will mean that there will be an unbalance in the lines supplying and returning from the hydraulic servomotor 14. With the cross-sectional area of-the supply port 46 being increased and the return port 50 being decreased in cross-sectional area there will be a tendency for a fluid pressure to build up in the servomotor 14 on the lower side of the piston 26. The decreasing of the supply port cross-sectional area on port 47 and an increase in the return port crosssectional area of port 51 will be etfective to cause a decrease in pressure on the upper side of the piston 26. With these unbalanced pressures acting on the piston 26 the piston rod will tend to move in an upward direction.

Movement of the spool 80 toward the left within the ported member 71 of the valve assembly 22 will cause a corresponding variation in the cross-sectional areas of the upstream inlet and outlet ports. Thus, the return port 77 will have in increased area as the member 81 moves toward the left and the supply port 73 will have a decreased area as the member 83 moves toward the left. Similarly, supply port 72 will have an increased area as the member 84 moves toward the left and the return port 76 will have a decreased area as the member 86 moves toward the left. With the decrease in the area of supply port 73 and an increase in the return port 77, the fluid pressure present on the upper side of piston 36 due to the fluid flowing through lines 180 and 181 will be decreased. With the increased cross-sectional area of the ports 72 and 75 and the decreased cross-sectional area of the return ports 76 and 78, the hydraulic fluid pressure on the lower side of the piston 76 will be effectively increased. With a greater pressure on the lower side of piston 36 than on the upper side, the piston will move in an upward direction.

With both pistons 26 and 36 moving in an upward direction piston rods 27 and 37 will act upon the respective interconnecting linkages 16 and 17 and will effect closing of the eyelids 11 and 12. As the piston rods move in an upward direction, the link members 106 and 110 will act on the pivoted followup members 104 and 108 causing the member 104 to pivot in a clockwise direction and the member 108 to pivot in a counter-clockwise direction. When the member 104 pivots in a clockwise direction the link 107 acting upon the link member 100 will cause this link member 100 to pivot in a counterclockwise direction about the pivot 102 so that the right end thereof will move in an upward direction. When the followup member 108 pivots in a counter-clockwise direction the link 111 will cause the member 101 to pivot in a clockwise direction about the pivot 103 so that the left end thereof will move in an upward direction. The connecting links 112 and 113 will then move in an upward direction and cause the pivoted member 113 to move in an upward direction and, as long as the forces of the servomotors remain equal, there will be no pivoting action of the pivoted member 114. The upward movement of the pivoted member 114 will cause the link 121 to pivot the crank arm 123 in a clockwise direction and will cause the link 122 to pivot the bell crank arm 124 in a counterclockwise direction. When crank arm 123 moves in a clockwise direction the actuating rod 62 will be moved back toward the left so that the spool 55 will be moved back to the balanced or centered position. The same type of movement will be found in valve assembly 22 where the counter-clockwise movement of the bell crank 124 will cause the actuating rod 89 to move the spool 80 back to the balanced position.

As soon as the temperature of the resistance element 157 has been increased to the desired value the motor 18 will be rotated in the opposite direction and the yoke 95 will be moved in a downward direction. This downward movement of the yoke 95 will be effective to cause the bell crank arm 123 to move in a clockwise direction and the crank arm 124 to move in a counterclockwise direction so that there will be effective unbalance of the cross-sectional areas of the parts of the respective pilot valve assemblies opposite to that first assumed. This will mean that a pressure will be built up on the upper side of the piston 26 and a similar pressure will be built up on the upper side of the piston 36 and the pistons will be caused to move in a downward direction. This downward movement of the pistons will move the eyelids back to their originally assumed positions, neglecting any droop in the system, and the piston rods will also be effective to rebalance the spools 55 and 80 as the pivoted followup members 104 and 108 are repositioned. The system is thus back in the position originally assumed.

It will be obvious that if there is a temperature change in the opposite direction the operation of the control system will be opposite to that assumed above.

Inasmuch as it is desired that the eyelids 11 and 12 not get out of step and not become twisted so as to unbalance the jet stream leaving the end of the engine 10, the interconnecting linkage 20 comes into play. Assume that there has been a temperature drop and the motor 18 has been effective to move the yoke in a downward direction. Assume also that for some reason or other the rod 17, associated with the servomotor 15, has stuck. Initially, movement of the yoke 95 in a downward direction will cause an equal and opposite rotation of the bell crank arms 123 and 124, the bell crank arm 123 moving in a counterclockwise direction and the crank arm 124 moving in a clockwise direction to move the spool 55 toward the right and the spool 80 toward the left. This will be effective to cause a decrease in pressure on the upper side of the piston 26 and an increase in pressure on the lower side of the piston 26 so as to tend to cause the piston rod 27 to be moved in an upward direction. Similar unbalance in pressures will exist in the servomotor 15 where there will be an increased pressure on the lower side of the piston 26 and a decrease in pressure on the upper side thereof. With the rod 17 stuck, however, there will be no movement of the piston rod 37. With the rod 27 free to move, the rod will move in an upward direction and will start to operate on the eyelids 11 and 12. Movement of the rod 27 in an upward direction will cause the rebalancing pivoted link 104 to be moved in a clockwise direction and the link to be moved in a counterclockwise direction. The pivoted link 108, however, associated with the other servomotor will remain in a fixed position and there will be no corresponding movement thereof.

This will mean that the counter-clockwise movement of the link 100 will cause the pivoted member 114 to be pivoted about the pivot point 116, associated with the other followup linkage from motor 15. This pivoting of the member 114 will be in a clockwise direction and the bell crank arm 123 will be moved in a clockwise direction while the crank arm 124 will also be moved in a clockwise direction. Movement of the crank arm 123 in a clockwise direction will cause the spool 55 to be moved back to a balanced position and movement of the crank arm 124 will cause the spool 80 to move in a further unbalanced direction. Thus further unbalance in the pilot valve assembly will further decrease the crosssectional area of the supply port 73 and will increase the cross-sectional area in the supply port 72. Similarly, the return port 77 will be increased in area while the return port 76 will be decreased in area. This further unbalance will cause a further increase in pressure on the lower side of the piston 36 and a further decrease in pressure on the upper side of the piston 36. This increase 111 pressure will normally be effective to break the rod 17 loose and as soon as it does break loose, the followup mechanism and linkage will be effective to get the servomotors back in step so that the operation will be effectively synchronized.

It will be obvious that if the sticking should have occurred at the servomotor 14, instead of the motor 15, there would have been a corresponding rebalance of the pllot valve 22 and an unbalancing of the valve 21 to effect the breaking loose of whatever might be causing the motor 14 to remain stationary.

While the slaving operation has been discussed in connection with a sticking piston, it should be noted that there are other factors which may cause the pistons to want to get out of step. For example, the pumps and 151 may have different outputs or there may be irregularities in the loading on the eyelids while they are being positioned. The slaving linkage will always maintain the pistons in step even when these conditions exist. Further, the gain in the slaving and follow linkage may be varied to maintain the error between the two pistons at a minimum by adjusting the multiplying ratios of the levers in the linkage.

It will be seen that the pilot valves 21 and 22 in providing modulation of the pressure drops in all of the fluid lines supplying and returning from the hydraulic servomotors makes possible very close control of the pressure drops within the valves and this will mean closer control on the hydraulic servomotors with less system lag and with greater pressure ranges available at the servomotor. This is particularly important where the slaving linkage 20 comes into play to maintain the motors in step.

Should it be desired to manually position the pilot valves 21 and 22, the latch release lever 140 will be operated. This will cause the latch release mechanism 138 to pivot the latch 135 in a clockwise direction about the pivot point 136. This will move the latch away from the member 134 so that the right end of the member 132 may be moved. When the push rod 143 moves out of engagement with the surface 144, the switch 142 will effectively open circuit the power lead 162 so that no power will be supplied to the amplifier 160. This will mean the motor 18 will be disabled and the member 132 will be free to pivot about the motor link connection 131, the motor being effectively locked when the system is deenergized clue to the internal gear train, not shown. The movement of the manual lever 19 will cause cor responding movement of the member 132 and the yoke 95 of the slaving linkage 20. The apparatus will, insofar as the hydraulic portion is concerned, operate in the manner assumed above when the motor 18 was positioning the member 132.

As soon as it is desired to switch the apparatus back to the automatic mode of operation, the release mechanism will be moved back to the position shOWn upon the drawing and the lever 19 will be moved until the support member 134 engages the latch on the end of the latch member 135. As soon as the member 134 and the latch member 135 are in engagement, the switch 142 will be operative to close the electrical circuit to the motor 160 and the apparatus will then be back in the position in which it is shown upon the drawing.

From the foregoing it will be understood that there has been provided a hydraulic control system wherein the hydraulic fluid is continuously circulated for cooling purposes through the system and the fluid pressure drops are modulatingly controlled in all of the supply and return lines to affect an optimum of control. Further, there has been provided a slaving mechanism which is effective to maintain the operation of a pair of servomotors in step, with that mechanism being effective when one of the motors does not operate to rebalance the control mechanism associated with the other motor and further unbalance the mechanism controlling the motor which is not operating until the condition is corrected. While many modifications will be obvious to those skilled in the art, it is intended that the scope of the present invention be limited solely by the appended claims.

I claim as my invention:

1. A hydraulic control apparatus, comprising in combination, a pair of cylinders having an inlet port at either end thereof and an outlet port at either end thereof, a pair of supply lines connecting said inlet ports to a source of fluid under pressure, a pair of return lines connecting said outlet ports to a fluid reservoir so that there will be a continuous flow of fluid through said cylinders, simultaneously acting valve means connected in each of said supply and return lines, means for modulating the movement of said valve means, a piston arranged within each cylinder for movement therein in accordance with pressures in said cylinders due to the pressure drops in said lines caused by said valve means, and mechanical adjusting means associated with said pistons for adjusting said valve means to maintain said pistons in step.

2. A hydraulic control apparatus, comprising in combination, a pair of hydraulic servomotors, a source of hydraulic fluid under pressure, a pair of feed lines interconnecting said source and each of said servomotors and a pair of return lines interconnecting said servomotors and said source so that there will be a continous flow of fluid through said servomotors, separate valve means associated with the feed and return lines of each of said motors for individually modulating the flow of fluid through said motors, motor means for simultaneously and modulatingly adjusting both of said valve means, and rebalance means including a plurality of mechanical links actuated by said servomotors for positioning each of said valve means.

3. A hydraulic control apparatus, comprising in combination, a pair of hydraulic servomotors having pistons arranged for movement within said motors, a source of hydraulic fluid under pressure, feed lines interconnecting said source and said motors and return lines interconnecting said motors and said source so that there will be a continuous flow of fluid through said motors, separate valve means associated with each of said motors and connected in said feed and return lines for modulatingly varying the fluid pressure drops in said feed and return lines, mechanical adjusting means for simultaneously varying the adjustment of said valve means, and means moved by said pistons for rebalancing the movement of said adjusting means.

4. A hydraulic control apparatus, comprising in combination, a pair of hydraulic servomotors having pistons therein, a source of hydraulic fluid under pressure, feed and return lines interconnecting said source and said motors so that there is a continuous flow of fluid through said motors, valve means associated with each of said feed and return lines for modulating the fluid pressure drops therein, means for simultaneously adjusting the valve means in the feed and return lines of each of said motors, a rebalancing linkage interconnecting said pistons and said valve means, said linkage having a plurality of interconnected mechanical links arranged to adjust said valve means to maintain the movement of said pistons in step.

5. A hydraulic control apparatus, comprising in combination, first and second servomotors, said servomotors each having a piston therein, a source of hydraulic fluid under pressure, feed lines and return lines interconnecting said source and said first and second motors to supply a continuous fiow of fluid through said motors, first and second valve means each connected in the respective feed and return lines to said first and second motors to modulatingly vary the flow of fluid through said lines, adjusting means for simultaneously positioning said first and second valve means, said adjusting means comprising a pivoted member which is pivoted at the center thereof and means connecting the ends thereof to the adjusting means of said first and second valve means, rebalancing means positioned by each of said pistons, said rebalancing means being connected to said pivoted member on either side of said pivot, and means including said rebalancing means and said pivoted member for maintaining the movement of the pistons of said first and second motors in step.

6. A hydraulic control apparatus, comprising in combination, a pair of hydraulic motors having pistons therein, a source of hydraulic fluid under pressure, feed lines interconnecting said source and said pair of motors, separate valve means in the feed lines to each of said motors, means for simultaneously adjusting both of said valve means, said last named means comprising a pivoted member pivoted at the center thereof on a movable pivot, a yoke member, linkage means interconnecting the yoke ends to points on said member on either side of said pivot, control means for adjusting said yoke to effect movement of said pivot, rebalance means acting through said yoke and said linkage to effect lateral movement of said pivot when said pistons are in step and pivoting said member when said pistons are not in step.

7. A hydraulic control apparatus, comprising in com bination, a pair of hydraulic servomotors, a source of hydraulic fluid under pressure, feed lines interconnecting said source and said motors, valve means connected in fluid pressure controlling relation to the fluid in said feed lines, a mechanical linkage arranged to simultaneously adjust all of said valve means, electrical motor means connected to variably position said linkage, manual means for positioning said linkage, spring biased latching means for maintaining said manual adjusting means ineffective, a manual release means for removing the effect of said latching means, switch means actuated upon said latching means being removed to electrically deenergizc said motor, and means including said switch means preventing reenergization of said motor until said apparatus has been reset.

8. A motor control apparatus for adjusting a pair of eyelids which are arranged to vary the outlet area of a combustion engine, the combination comprising, a pair of motor means, one of. said pair arranged to be mounted at one side of the engine and the other of said pair arranged to be mounted on the opposite side of the engine with means interconnecting each of the motor means to both of said eyelids for positioning the same in an opening or closing direction, control means connected to modulatingly control the effect of each of said motors upon said eyelids, and means interconnecting said motors and said modulating control means for maintaining said motors in step.

9. A control apparatus for a combustion engine having a pair of eyelids for varying the outlet area thereof, the combination comprising, a pair of hydraulic motors arranged to be mounted adjacent said engine on either side thereof, a source of hydraulic fluid under pressure, fluid lines interconnecting said source and said motors for continuously circulating fluid through said motors, separate valve means connected to the lines feeding each of said motor means, adjusting means for simultaneously modulatingly adjusting said separate valve means to etfect movement of said motors, and interconnected rebalancing means operated by each of said motors for acting upon said valve means to maintain said motors in step.

10. Control apparatus for a combustion engine having a pair of eyelids for adjusting the outlet area thereof, the combination comprising, a pair of hydraulic motors, a source of hydraulic fluid under pressure, fluid lines interconnecting said source and said motors so that there is a continuous flow of fluid through said motors, separate valve means connected in each of said lines for modulatingly varying the fluid pressure drops in said lines, means for simultaneously adjusting said separate valve means, said means comprising a temperature responsive control system, said simultaneously adjusting means also including rebalancing means individually actuated by said motors, and interconnecting means including said rebalancing means for maintaining the operation of said motor in step.

11. A pair of control motors each having its output means arranged to position separate controllers, power control means connected to said motors to individually control the actuation of said motors, rebalancing means individually positioned by said output means, said rebalancing means being connected to said power control means to cancel the effect thereof upon said motors as said motors are actuated, and interconnecting slaving means connected in said rebalancing means, said slaving means maintaining the operation of said motors in step.

12. A pair of fluid motors having their output means arranged to position separate controllers, fluid control means connected to said motors to variably adjust the pressures of the fluid acting on said motors, rebalancing means connected to said output means and to said control means to adjust the effect of the latter upon said motors as said motors are adjusted, and interconnecting slaving means included in said rebalancing means, said slaving means acting upon said control means to vary the fluid pressures acting on said motors if necessary to keep said motors in step.

13. A pair of fluid motors having their output means arranged to position separate controllers, separate fluid control means connected to each of said motors to variably adjust the pressures of the fluid acting on said motors, adjusting means for simultaneously acting upon said control means, rebalancing means connected between each of said output means and each of said control means to eliminate the eflect of said adjusting means as said motors are positioned, and interconnecting slaving means included in said rebalancing means, said slaving means cooperating with said rebalancing means to rebalance the control means connected to one of said motors and unbalance to a greater degree the control means connected to the other of said motors when the positioning of said other motor lags behind that of said one motor.

References Cited in the file of this patent UNITED STATES PATENTS 1,952,806 Hyland Mar. 27, 1934 2,364,128 Carlson Dec. 5, 1944 2,477,452 Guins July 26, 1949 2,507,581 Waters et al. May 16, 1950 2,514,248 Lombard et al. July 4, 1950 2,597,361 Mott May 20, 1952 FOREIGN PATENTS 19,484 Switzerland Feb. 20, 1900 

